1. Field
The invention relates to an apparatus for treating water by means of an electric field. The apparatus has a treatment chamber. An anode and a cathode is arranged in this treatment chamber. When a preferably inhomogeneous electric field is applied between the anode and the cathode, seed crystals of minerals contained in the water are formed on the cathode. These seed crystals are separated from the cathode and carried away with the flowing water.
2. State of the Art
Drinking water contains essential minerals, among others calcium and magnesium carbonates. Such minerals, in total, are called water hardness. On one hand, such minerals are important to health. On the other hand, they may cause malfunction of the drinking water installation, in particular if the water is heated. When the water is heated in a drinking water heater, for example, insoluble lime depositions, also called boiler scale, are formed. This boiler scale is formed on the warm side of the installation. Boiler scale impedes heat transmission. In tubes, the boiler scale, over time, may result in closure of the tube installation downstream of the drinking water heater.
In order to avoid such deposits of boiler scale, the water can be “softened”. This softening process removes the minerals from the drinking water. Such softening can be achieved by ion exchange or reverse osmosis. This avoids the deposit of boiler scale. In exchange therefor, however, the quality of the drinking water is reduced by the removal of the minerals, which, for other reasons, are desirable.
Methods of treating drinking water by means of so-called “electro-physical” apparatus cause the formation of seed crystals in the drinking water, which are then carried away by the drinking water. The formation of the seed crystals result in the drinking water thus treated causing less build up in the form of boiler scale, while the minerals in the drinking water are retained.
The treatment by means of electro-physical apparatus is substantially based on the following principle:                Drinking water always contains a certain proportion of carbon dioxide (CO2) dissolved therein. This carbon dioxide forms a reaction equilibrium with the remaining components, calcium hydrogen carbonate (Ca(HCO3)2 being formed from CaCO3 in accordance with the reaction equationCaCO3+H2O+CO2Ca(HCO3)2        
If the water is heated, CO2 will escape from the water and boiler scale will be formed. It is, however, also possible to change purposefully the lime-carbon dioxide equilibrium in the drinking water.
If carbon dioxide is supplied to the water, this will result in shifting the equilibrium to the left in the above equation. Seed crystals of calcium carbonate (lime over-saturation) are formed from the calcium hydrogen carbonate present in the water. Then the subsequently formed calcium carbonate will be deposited predominantly on the once generated seed crystals, i.e. the seed crystals “grow”.
This reaction is caused electrolytically in a treatment chamber containing a cathode and an anode. The seed crystals are formed on the cathode. The seed crystals have to be added to the drinking water after they have grown sufficiently. Then carbonate is already present in the form of seed crystals in the drinking water, when the drinking water is heated. There is no need of generating seed crystals anew. Accordingly, the carbonate will be deposited predominantly on the seed crystals carried away in the water rather than on the installation elements.
EP patent application 0,751,096 discloses an apparatus for the electro-physical drinking water treatment by means of an electric field wherein an electric field inhomogeneous in space is generated by an ac voltage superimposed on a dc voltage.
From EP 1 076 038 A2 an apparatus for electro-physical treatment of drinking water by means of an electrical field is known, in which a field inhomogeneous in space is generated using a cathode consisting of a plurality of metal pins. The pins extend through a perforated disc. The crystal seeds formed at the surface of the pins are mechanically removed by means of a motor. It is an object of this procedure to achieve a long dwell time of the seeds at the surface of the electrodes. An after-treatment chamber is arranged around the cathode consisting of the pins. Vertical graphite electrodes are arranged in the after-treatment chamber in a circular array. The graphite electrodes alternately are polarized as an anode and a cathode. Each of the electrodes therefore has two neighboring electrodes oppositely polarized. The electrodes in the after-treatment chamber change their polarization in regular time intervals.
The production of the known arrangement is expensive. The pins required for the generation of the inhomogeneous field need to be manufactured by hand. The insertion of the perforated disc is time consuming. Furthermore, the cathode is blocked after a while and must be cleaned. Therefore the apparatus has to be disassembled and the cathode has to be cleaned and inserted back into its place. This is expensive and time consuming also.
Furthermore, there is a known apparatus for the electro-physical treatment in which a voltage is applied to a granular mixture from graphite and silica sand. In this mixture the crystal seeds are generated. However, the granular mixture also acts as a filter and is blocked after long treatment durations. It then has to be replaced or serviced.